Telomeres generally refer to specific DNA-protein structures located at each end of a chromosome, which protect the end of the chromosome from unnecessary deterioration, repair and inter-chromosomal fusion. In normal cellular process, cells divide and lose a portion of the telomeres in each cell division. The length of a telomere is reduced each time, i.e. telomere shortening. When a telomere length reaches a limit, i.e. becomes too short to exhibit the protective effect of a telomere, the cell undergoes programmed cell death and eventually dies.
Telomerase, also known as telomere terminal transferase, is a reverse transcriptase enzyme that synthesizes telomeric DNA sequences and adds the DNA sequences to the 3′ end of telomeres. It keeps the telomere from wearing down too much by maintaining the length of the telomere. I.e. telomerase counteracts with telomere shortening. Notably, it has been found that telomerase is highly activated, i.e. overly expressed, in most cancers and immortalized cells. Telomerase facilitates the elongation of the telomeres and keeps cancer cells immortal. Accordingly it is believed that inhibiting the activity of the telomerase and reactivating telomere shortening help to trigger programmed cell death of the cancer cells and is a suitable approach for treating cancer.
Telomeric G-quadruplexes which are formed spontaneously by telomeric DNA folding may hinder the recruitment of telomerase. Studies have confirmed that a stabilization of telomeric G-quadruplexes via non-covalent interaction with small organic molecules is a suitable way to inhibit telomerase activity. For characterizing the interaction between small organic molecules and telomeric G-quadruplexes, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) is usually applied owing to its sensitivity and reliability to determine stoichiometries, relative binding affinities (RBA) and equilibrium association constants of drug-DNA complexes.
As there remains a strong need for therapeutically effective compounds and improved ways for successfully treating cancer and in view of the highly promising approach of an inhibition of telomerase activity, having new compounds with sufficient telomerase activity is highly desirable. As usual, it would generally be desirable to have compounds with reduced risk for side effects, which can be prepared in a cost-effective way and are directed only at tumor cells.
Recently, Traditional Chinese medicine as well as complementary and alternative medicine has getting popular providing a lot of treatment options. Traditional Chinese medicines based on plant materials as well as plants or respective components gained from plants usually allow for treatment of various diseases and conditions while bearing a reduced risk for side effects. In view of the rich medicinal plant resources, available respective medicines can usually be produced in a cost-effective way. Accordingly, there has been a lot of research with regard to plants and respective ingredients for treatment of several diseases and conditions.
For example, Tylophora atrofolliculata (Asclepiadaceae) is already used as a traditional medicine. The roots of Tylophora atrofolliculata which are mainly distributed in the Guangxi Province in the Southwest of China have been used such as for the treatment of rheumatism. Components isolated from said plant include phenanthroindolizidine alkaloids (Huang, X. et al., Planta Med., 2004, 70, 441-445, Abe, F. et al., Chem. Pharm. Bull, 1998, 46, 767-769, Abe, F. et al., Phytochemistry, 1995, 39, 695-699, Ali, M. et al., J. Nat. Prod., 1991, 54, 1271-1278, M. Ali and K. K. Bhutani, Phytochemistry, 1987, 26, 2089-2092, Ali, M. and Bhutani, K. K., Phytochemistry, 1989, 28, 3513-3517, Bhutani, K. K. et al., Phytochemistry, 1985, 24, 2778-2780, Dhiman, M. et al., Chem. Pap.-Chem. Zvesti, 2013, 67, 245-248), however, only alkaloids such as tylophoridicine C-F, tylophorinine, tylophorinidine have been isolated from this plant so far. Members of the phenanthroindolizidine alkaloid class are generally well known to possess multiple pharmacological effects, such as anti-inflammatory, antifungal, antibacterial, and antiviral activities. Besides, pronounced cytotoxicity of some phenanthroindolizidine alkaloids against various cancer cell lines attracted much attention in the discovery of anticancer drugs (Lee, Y. Z. et al., Planta Med., 2011, 77, 1932-1938, Cai, X. F. et al., J. Nat. Prod., 2006, 69, 1095-1097, Damu, A. G. et al., Planta Med., 2009, 75, 1152-1156, Damu, A. G. et al., J. Nat. Prod., 2005, 68, 1071-1075, Lykkeberg, A. K. et al., J. Nat. Prod., 2002, 65, 1299-1302).
In view of the presence of various different compounds in plants usually with completely different mode of action and therapeutic efficiency, there is a strong need for identifying and providing components in isolated form with suitable therapeutic efficiency such as with sufficient telomerase inhibitory activity for treatment of cancer. Having those active ingredients in isolated form could further reduce the risk of side effects or interactions resulting from the presence of further compounds limiting the therapeutic use.